Callback Asp.Net Mystery

I'm facing a strange thing with Asp.Net and initiating callback to update a portion of the page containing a grid.

The problem is, it seems I can't update any other portion in the page nor can I add anything to the response body. I simply want to show an error message in case updating the grid fails. And mind u, even javascript fails to appear in the page after the callback.

I even tried redirecting to a separate error page but the response object seems to have no headers and can't redirect to any page!!

I hope I can post a solution for this, sure there's something I'm missing :(
Got any ideas?!